1Departments of Agronomy, Soil Science and Agriculture Engineering, College of Agricultural and Life Sciences and Cooperative Extension Service, University of WisconsinMadison, WI 53706.
2Department of Agronomy and Plant Genetics, University of Minnesota, St. Paul, MN 55108. May, 1990.
The castorbean plant (Ricinus communis) has been cultivated for centuries for the oil produced by its seeds. The Egyptians burned castor oil in their lamps more than 4,000 years ago.
Thought to be native to tropical Africa, the plant is a member of the spurge family. The seeds with hulls removed contain 35 to 55% oil. The seeds, leaves, and stems of the plant contain ricin and ricinine, which are poisonous to humans and animals. Eating a castorbean causes nausea, and eating several may cause death. These toxic compounds are not present in the oil.
Castorbeans are grown on a limited scale in the United States. Demand for the crop peaked in the early 1950s, when the federal government wished to increase supplies of castor oil for military applications in the event of a national emergency. The government guaranteed farmers, particularly in the Southwest, ten cents per pound for the seeds, which were grown under contract with castor oil processors.
The castorbean plant grows well in soil of medium texture. It is best adapted to southeastern Kansas, Missouri, southern Illinois, southern Indiana, Tennessee, Kentucky, and parts of Oklahoma and Texas. With irrigation, it also grows well in the Southwest.
In the United States, castor oil has been used by the military in aircraft lubricants, hydraulic fluids, and in the manufacture of explosives. It has also been used in the synthesis of soaps, linoleum, printer's ink, nylon, varnishes, enamels, paints, and electrical insulations. Textile scientists have used sulphonated castor oil in the dyeing and finishing of fabrics and leather. The most infamous application of castor oil may have been as a purgative popular for the treatment or prevention of many ailments in the first half of the twentieth century.
Castorbean meal is included as a protein source in feed for swine. Castorbean pomace, or meal, the residue left after the oil has been extracted from the seeds, has been included in mixed fertilizer. This product contains the ricin and ricinine from the seeds. Certain varieties of castorbean plants are grown as ornamentals.
In the tropics, the castorbean plant is a perennial. It is grown as an annual in temperate regions, however, requiring a growing season of 140 to 180 days.
Germination is slow. Seedlings will emerge 10 to 21 days after planting. Commercial varieties grow to a height of 3 to 10 ft.
The plant consists of several stems or branches, each terminated by a spike. The mature spike is six to 12 in. long. In some varieties, female flowers are on the upper part of the spike and male flowers on the lower part. Other varieties have male and female flowers interspersed on the spike. Varieties with spikes of only female flowers have made possible the production of hybrid seed. Male flowers drop off the spike after pollination.
The lower spikes on the plant mature first, followed by the upper spikes. Each spike bears 15 to 80 capsules, which may be prickly or smooth on the outer surface. The capsules, which develop from the female flowers, contain three seeds each and explode when ripe.
The seeds may be egg-shaped, oblong, or round, usually with an enlargement on one end, called the caruncle. Seeds vary in size, but most commercial varieties average 1,000 to 1,500 seeds/lb.
The plant is not a legume, as its name would imply. It has no soil-improving value other than that of any rotation crop.
Castorbeans grow best where temperatures remain fairly high throughout the growing season of 140 to 180 days. The soil must be able to warm up early in the spring. The seed may fail to set, however, if the temperature stays above 100°F for an extended period.
The crop requires a loamy soil of medium texture. Castorbeans do well on either alkaline or acid soils, as long as the subsoil is permeable and there is good drainage. Seed will not set if soil moisture is inadequate. Castorbeans should not be planted in an area that is subject to erosion.
Seeds should be cleaned to remove foreign material, seeds with attached hulls, and damaged seeds. They should also be treated with a fungicide before planting. This is particularly important where there is a risk of low spring temperatures and high soil moisture immediately after planting. Thiram is the only registered seed treatment fungicide for use on castorbeans.
Castorbeans are poisonous for animals and humans. In addition, inhaling dust from the seeds may cause allergic reactions in some individuals. Seed treatment should be performed carefully to minimize dust and to avoid contamination of food and livestock feed. Children should be kept away from castorbean storage areas, and adults working with the seeds and plants should be warned of their poisonous properties.
To prepare the seedbed, plow or disk the land. Be sure the soil is moist at the planting depth of one to three in.
Castorbeans should be planted in early May, about the same time as corn. Seedlings will emerge in 10 to 21 days.
Good stands of castorbeans require fairly heavy planting rates, because germination of the seed is usually rather low. Seeding at 10 to 14 lb/acre will give a good stand, depending on the seed size and the height of the variety. Row width should be 38 to 40 in. with 8 to 12 in. between plants. Because of differences in germination rates and plant size, growers should calculate rates based on the seed lot. Seeds should be planted at a depth of 1 1/2 to 3 in.
Because castorbeans are oily and easily broken, they can clog machinery and cause irregular spacing. Most corn planters with an air metering system should perform well. Planters using metering plates will require plates with proper cell size. Always check the planting unit to ensure that excessive bean cracking or crushing is not occurring during planting.
Castorbeans grow well on slightly alkaline or acid soils. The most important factor in fertility level is the supply of nitrogen in the soil. Insufficient nitrogen results in reduced castorbean yields. Excessive nitrogen produces heavy vegetative growth with little or no increase in seed yield.
The amount of nitrogen required by castorbeans depends on the soil organic matter content, as shown in Table 1. Preplant and sidedress applications of nitrogen may be beneficial at the higher application rates or on lighter-textured soils.
In general, castorbeans require the same amount of nutrients as other low-demand field crops. For typical silt loam soils testing in the optimum range (6 to 10 ppm P; 81 to 100 ppm K), approximately 20 lb P2O5 and 40 lb K2O should be applied per acre. If soil tests are below optimum, approximately 5 lbs P2O5 and 20 to 30 lb K2O should be applied in addition to the previous amounts. Castorbeans do not generally respond to phosphorus, and excess soil phosphorus levels can actually decrease yields. Therefore, do not apply P2O5 except where soils test in the optimum or below optimum level for extractable P.
Table 1: Nitrogen recommendations for castorbeans.
Castorbean varieties have been developed to produce large yields of seed with a single harvest. The tall varieties may reach a height of 10 ft or more. The dwarf types seldom exceed four or five ft.
No information is available about the adaptability of varieties to the Upper Midwest.
The slow emergence and early growth of castorbeans means the plants are not strong competitors against weeds. Rotary hoeing during the first few weeks after planting, followed by row cultivation should provide acceptable control. Because the main lateral roots of the castorbean plant are near the soil surface, cultivation should be shallow. At the present time, herbicides are not registered for controlling weeds in castorbeans in Wisconsin or Minnesota.
Resistance to various diseases varies among castorbean varieties. During periods of heavy rains or dews, capsule molds, Alternaria leaf spot and bacterial leaf spot may occur. Alternaria leaf spot is more severe in nitrogen-starved plants. Other diseases may occur, particularly in wet seasons. To help prevent disease problems, a good rotation program and treatment of seed with a fungicide prior to planting are recommended. Thiram is the only registered seed treatment fungicide.
Though leaf- and stem-feeding insects usually do not cause serious damage to castorbean plants, cutworms and wire worms may reduce stands. Stink bugs, corn earworms, webworms, caterpillars, grasshoppers, thrips, spider mites, leaf miners, Lygus bugs, the yellow-striped army worm, and the European corn borer also may attack the plants.
The castorbean crop is ready for harvesting when all the capsules are dry and the leaves have fallen from the plants. Ideally, harvesting should begin 10 to 14 days after the first killing frost. If killing frosts will not permit completion of harvesting before winter, a chemical defoliant may be applied 10 to 15 days ahead of the desired harvest date. Defoliants tend to reduce yields, however. Delay in harvesting after the crop is ready may result in losses from "shattering," in which the seeds pop out of the capsules.
Since castorbeans are very susceptible to cracking and splitting during harvest, adjustment of the combine cylinder speed and cylinder-concave clearance is very important. Usually, a low cylinder speed and wide cylinder concave clearance are recommended. Combine operators should frequently inspect harvested beans for breakage.
Weeds cause problems in the castorbean harvest. They may clog machinery or push in front of the harvester and cause shattering of the castorbeans. Volunteer corn plants present no special problem in the harvesting operations, but do add foreign material to the yield.
After harvest, break up the stalks mechanically and work them into the soil. The stalks deteriorate rapidly and furnish organic matter. Castorbean hulls, which are scattered over the field during harvest, are about equal to barnyard manure in fertilizer value.
Seeds left in the field after harvest may cause a volunteer problem in the next year's crop. Waiting until seeds germinate and then disking the young plants down will prevent this to some extent. Follow castorbeans with a row crop or a grain crop, for which the volunteer castorbean plants will not present a problem.
Moisture content, foreign material, and cracked or broken beans are considered in grading the seed. Ideally, castorbeans should be stored at less than 6% moisture.
Yields vary depending on variety, the season, cultural conditions, and the care exercised in harvesting. No information is available concerning castorbean yields in Wisconsin and Minnesota. However, yields of about 2,200 lb/acre have been produced in Nebraska tests.
Castorbean markets are limited. The crop should be grown only after identifying a market, and preferably after arranging a contract with a buyer.